# Isoprene Aerosol Growth in the Upper Troposphere: Application of the Diagonal Volatility Basis Set to CLOUD Chamber Measurements

## TL;DR

This study explores how isoprene particles grow in the upper atmosphere and finds that a few low-volatility compounds drive their early growth.

## Contribution

The study applies the diagonal volatility basis set to CLOUD chamber data to identify key species and processes in isoprene particle growth.

## Key findings

- Kinetically limited condensation of a few species dominates particle composition and growth.
- Particle-phase processes like oligomerization and hydrolysis do not affect early growth.
- dVBS predictions explain 90% of measured growth under cold, low-acid conditions.

## Abstract

Isoprene oxygenated organic molecules (IP-OOM) can nucleate new particles in the upper troposphere. These particles may grow into cloud condensation nuclei and influence the clouds and climate. However, little is known about the individual species driving growth and whether they undergo condensed-phase reactions. We conducted isoprene oxidation experiments at 223 and 243 K in the CLOUD chamber at CERN. Gas-phase concentrations were measured with chemical ionization mass spectrometers (NO3
–-CIMS, Br–-MION2-CIMS, and NH4
+-CIMS). Growth rates from 8 to 20 nm were measured by a Neutral Cluster and Air Ion Spectrometer. Particle-phase composition was measured by a filter sampling chemical ionization mass spectrometer. We use the diagonal volatility basis set (dVBS) analysis framework to compare gas- and particle-phase measurements and assess species and processes influencing growth. We find that kinetically limited condensation of a few species dominates particle composition and growth. Particle-phase processes, including oligomerization and organonitrate hydrolysis, do not influence the early growth. dVBS growth rate predictions can explain 90% of the measured growth, dominated by kinetic condensation of low-volatility species. Our findings indicate that initial growth of IP-OOM particles under cold, low-acid conditions may be controlled and modeled by the kinetically limited condensation of low-volatility compounds.